Crusader knight
Refers to a knight who participated in the Crusades. Historical term.
The Crusader knights fought aiming for the Holy Land.
十字軍 means 'the Crusades' or 'Crusader army', while 十字軍騎士 specifically refers to an individual knight within that army.
Compound of 十字軍 (Crusades) and 騎士 (knight).